Strain and Kinetics Control During Separation Phase of Imprint Process

ABSTRACT

Systems and methods for improving robust layer separation during the separation process of an imprint lithography process are described. Included are methods of matching strains between a substrate to be imprinted and the template, varying or modifying the forces applied to the template and/or the substrate during separation, or varying or modifying the kinetics of the separation process.

REFERENCE TO RELATED APPLICATION

This patent application claims the benefit of U.S. ProvisionalApplication Ser. No. 61/109,557, filed Oct. 30, 2008, and U.S.Provisional Application Ser. No. 61/108,131, filed Oct. 24, 2008, bothof which are incorporated by reference herein.

BACKGROUND INFORMATION

Nano-fabrication includes the fabrication of very small structures thathave features on the order of 100 nanometers or smaller. One applicationin which nano-fabrication has had a sizeable impact is in the processingof integrated circuits. The semiconductor processing industry continuesto strive for larger production yields while increasing the circuits perunit area formed on a substrate; therefore nano-fabrication becomesincreasingly important. Nano-fabrication provides greater processcontrol while allowing continued reduction of the minimum featuredimensions of the structures formed. Other areas of development in whichnano-fabrication has been employed include biotechnology, opticaltechnology, mechanical systems, and the like.

An exemplary nano-fabrication technique in use today is commonlyreferred to as imprint lithography. Exemplary imprint lithographyprocesses are described in detail in numerous publications, such as U.S.Patent Publication No 2004/0065976, U.S. Patent Publication No.2004/0065252, and U.S. Pat. No. 6,936,194, all of which are herebyincorporated by reference.

An imprint lithography technique disclosed in each of the aforementionedU.S. patent publications and patent includes formation of a reliefpattern in a formable liquid (polymerizable liquid) and transferring apattern corresponding to the relief pattern into an underlyingsubstrate. The substrate may be coupled to a motion stage to obtain adesired positioning to facilitate the patterning process. The patterningprocess uses a template spaced apart from the substrate and a formableliquid applied between the template and the substrate. The formableliquid is solidified to form a rigid layer (a solidified layer) that hasa pattern conforming to a shape of the surface of the template thatcontacts the formable liquid. After solidification, the template isseparated from the rigid layer such that the template and the substrateare spaced apart. The substrate and the solidified layer are thensubjected to additional processes to transfer a relief image into thesubstrate that corresponds to the pattern in the solidified layer.

In imprint technology, defects like sheared, pulled-out, and tornfeatures may be observed in resulting imprinted patterns. A defect oftenoccurs due to strain mismatch of the template and substrate duringseparation. The resulting patterned features may be tilted and/ordamaged, with the greatest effects often on the smallest features. Theseparation effects may also have radial dependence, Transition fromzones of high feature density to low feature density may also lead to alarge number of imprint defects, often the result of a sudden change inshear mismatch between the template and substrate.

Current imprint methods often use templates of arbitrary thickness andshape, as well as arbitrary thickness of wafers and disks (substrates).Also, separation phase imprint parameters like separation forces, tilt,pressures behind template and wafer, vacuum levels, and kinetics of allthe above parameters may not be taken into account in current imprintmethods with respect to improving the quality of imprinting.

BRIEF DESCRIPTION OF DRAWINGS

So that the present invention may be understood in more detail, adescription of embodiments of the invention is provided with referenceto the embodiments illustrated in the appended drawings. It is to benoted, however, that the appended drawings illustrate only typicalembodiments of the invention, and are therefore not to be consideredlimiting of the scope.

FIG. 1 illustrates a simplified side view of a lithographic system inaccordance with an embodiment of the present invention.

FIG. 2 illustrates a simplified side view of the substrate and templateshown in FIG. 1 having a patterned layer positioned thereon.

FIGS. 3A and 3B illustrate shrinkage of the contact area during aseparation event.

FIG. 4 illustrates schematically an interface between a rigid patternedtemplate (top) and a flexible substrate (bottom) with a replicated layerthereon.

FIG. 5 illustrates a simplified side view of a substrate having astiffening layer added to the surface of the substrate prior to theimprint process.

FIG. 6 illustrates a comparison between a wafer and a SOG wafer, whereinthe wafer has multiple separation defects.

FIGS. 7A and 7B illustrate template curvature and the correspondingshear strain of its surface depending on template feature density.

FIG. 8 illustrates a graphical representation of separation force overtime.

FIG. 9 illustrates a flow chart of an exemplary method for separating atemplate from a patterned layer while minimizing shearing and pullingstress

FIG. 10 illustrates a simplified side view of portions of thelithographic system shown in FIG. 1, including the substrate andtemplate having a patterned layer positioned there between.

FIG. 11 illustrates a flow chart of an exemplary method for separating atemplate from a patterned layer while minimizing shearing and pullingstress by employing feedback, monitoring, and tracking.

FIG. 12 illustrates various dummy fill pattern options.

DETAILED DESCRIPTION

Referring to the figures, and particularly to FIG. 1, illustratedtherein is a lithographic system 10 used to form a relief pattern onsubstrate 12. Substrate 12 may be coupled to substrate chuck 14. Asillustrated, substrate chuck 14 is a vacuum chuck. Substrate chuck 14,however, may be any chuck including, but not limited to, vacuum,pin-type, groove-type, electromagnetic, and/or the like. Exemplarychucks are described in U.S. Pat. No. 6,873,087, which is herebyincorporated by reference.

Substrate 12 and substrate chuck 14 may be further supported by stage16. Stage 16 may provide motion along the x-, y-, and z-axes. Stage 16,substrate 12, and substrate chuck 14 may also be positioned on a base(not shown).

Spaced-apart from substrate 12 is a template 18. Template 18 generallyincludes a mesa 20 extending therefrom towards substrate 12, mesa 20having a patterning surface 22 thereon. Further, mesa 20 may be referredto as mold 20. Template 18 and/or mold 20 may be formed from suchmaterials including, but not limited to, fused-silica, quartz, silicon,organic polymers, siloxane polymers, borosilicate glass, fluorocarbonpolymers, metal, hardened sapphire, and/or the like. As illustrated,patterning surface 22 comprises features defined by a plurality ofspaced-apart recesses 24 and/or protrusions 26, though embodiments ofthe present invention are not limited to such configurations. Patterningsurface 22 may define any original pattern that forms the basis of apattern to be formed on substrate 12.

Template 18 may be coupled to chuck 28. Chuck 28 may be configured as,but not limited to, vacuum, pin-type, groove-type, electromagnetic,and/or other similar chuck types. Exemplary chucks are further describedin U.S. Pat. No. 6,873,087, which is hereby incorporated by reference.Further, chuck 28 may be coupled to imprint head 30 such that chuck 28and/or imprint head 30 may be configured to facilitate movement oftemplate 18.

System 10 may further comprise a fluid dispense system 32. Fluiddispense system 32 may be used to deposit polymerizable material 34 onsubstrate 12. Polymerizable material 34 may be positioned upon substrate12 using techniques such as drop dispense, spin-coating, dip coating,chemical vapor deposition (CVD), physical vapor deposition (PVD), thinfilm deposition, thick film deposition, and/or the like. Polymerizablematerial 34 may be disposed upon substrate 12 before and/or after adesired volume is defined between mold 20 and substrate 12 depending ondesign considerations. Polymerizable material 34 may comprise a monomeras described in U.S. Pat. No. 7,157,036 and U.S. Patent Publication No.2005/0187339, all of which are hereby incorporated by reference.

Referring to FIGS. 1 and 2, system 10 may further comprise an energysource 38 coupled to direct energy 40 along path 42. Imprint head 30 andstage 16 may be configured to position template 18 and substrate 12 insuperimposition with path 42. System 10 may be regulated by a processor54 in communication with stage 16, imprint head 30, fluid dispensesystem 32, and/or source 38, and may operate on a computer readableprogram stored in memory 56.

Either imprint head 30, stage 16, or both vary a distance between mold20 and substrate 12 to define a desired volume therebetween that isfilled by polymerizable material 34. For example, imprint head 30 mayapply a force to template 18 such that mold 20 contacts polymerizablematerial 34. After the desired volume is filled with polymerizablematerial 34, source 38 produces energy 40, e.g., broadband ultravioletradiation, causing polymerizable material 34 to solidify and/orcross-link conforming to shape of a surface 44 of substrate 12 andpatterning surface 22, defining a patterned layer 46 on substrate 12.Patterned layer (solidified layer) 46 may comprise a residual layer 48and a plurality of features shown as protrusions 50 and recessions 52,with protrusions 50 having thickness h₁ and residual layer having athickness h₂.

The above-mentioned system and process may be further employed inimprint lithography processes and systems referred to in U.S. Pat. No.6,932,934, U.S. Patent Publication No. 2004/0124566, U.S. PatentPublication No. 2004/0188381, and U.S. Patent Publication No.2004/0211754, each of which is hereby incorporated by reference.

Robust Layer Separation

Still referring to FIGS. 1 and 2, strain differences in template 18 andsubstrate 12 lead to deformation of imprinted features, pull-outs, linecollapse, and/or other imprint defects during separation of the template18 and the substrate 12 after an imprint process. Strain and relatedstress may be based upon a geometry of template 18 and substrate 12,forces applied, and kinetics of the process. In one embodiment, thestrain and related stress is based solely upon a geometry of template 18and substrate 12, forces applied, and kinetics of the process. Stiffnessand Young modulus of the materials involved may be taken into account.Adhesion force between imprint material 34 and substrate 12, and betweenimprint material 34 and template 18, as well as friction between thepatterning surface 22 and resulting features on the substrate 12 duringseparation should be considered in a strain analysis. Variation offeature density on the patterning surface 22 of the template 18 play animportant role in crack propagation dynamics and significantly affectsresulting strains and quality of imprinting, including robust layerseparation.

Matching Strains

FIGS. 3A and 3B illustrate an example of two time moments t₁ and t₂during a separation process. For simplicity, consider a flexiblesubstrate (wafer) 301 and less flexible template 302, which isrelatively thick by comparison with flexible substrate 301. A constantforce F is applied to separate the template 302 and the substrate 301.In the illustrations in FIGS. 3A and 3B, the contact areas (shown as A₁and A₂) are the areas where the substrate 301 is in contact with thetemplate 302 during the separation process. As shown, the contact areaat time t₁ is A₁ and the contact area at time t₂ is A₂. The contact areaA₂ at t₂ is smaller than the contact area A₁ at t₁ (where t₂>t₁), as thetemplate 302 and the substrate 301 are pulled away from each other. Thestrain in the substrate 301 along the perimeter of the contact area A₂will be significantly greater than with contact area A₁, if the force Fapplied is not properly decreased while the contact area shrinks from alarger area A₁ to a smaller area A₂. This may increase the local stressthereof, and correspondingly, the local strain.

Shear stress along the substrate 301 surface may lead to surface strain,elongation, or compression along its surface. If the template 302 hasimprinted features upon the substrate 301, then the resulting strain mayshear the features off the substrate 301 during separation.

FIG. 4 schematically illustrates the area of separation between a rigidpatterned template 18 and a flexible substrate 12 with a replicatedlayer including features 50 on it. Typical feature height h is 100 nm.

One of the ways to minimize, if not prevent, the effect of uneven stressand strain during separation is to substantially match strains in thetemplate 18 and substrate 12. For example, matching strains may includematching the stiffness of the template 18 and substrate 12. Matchingstiffness may take into account the geometry of the template 18 andsubstrate 12, including the thickness of each. In one embodiment, thethickness of the substrate 12 is matched to the thickness of thetemplate 18, such that they have substantially equal thickness. As usedin this application, matching may include conforming, adjusting,adapting, modifying, fitting, tuning, or the like; such that the strainproperties are reasonably equal or equivalent, or such that a responsefrom the substrate 12 is the same or nearly the same as a response fromthe template 18 when equivalent forces are applied to each. Youngmodulus, orientation (tilt), and other factors may also be used tominimize, if not prevent, the effect of uneven stress and strain duringseparation.

In one embodiment (shown in FIG. 2), matching the stiffness of thetemplate 18 and substrate 12 may be accomplished by increasing thethickness h₂ of the residual layer 48. Residual layer 48 is the resultof positioning polymerizable material 34 upon substrate 12 during theimprint process. Additional polymizerable material 34 may be positionedupon substrate 12 during the imprint process to build up the overallthickness of the substrate 12, thereby changing the overall geometry andstiffness characteristics of the substrate 12, and reducing the pullingstress and/or shearing stress during separation of the template 18 andthe substrate 12. In an exemplary embodiment, a predetermined amount ofpolymerizable material 34 is positioned on substrate 12 that iscalculated to produce a desired geometry and/or desired stiffness and/orstress characteristics.

In an embodiment illustrated in FIG. 5, a stiffening layer 100 may beadded to the surface of substrate 12 prior to the imprint process. Forexample, the stiffening layer 100 may be an organic layer, such as aSpun On Glass (SOG) layer, or the like. The stiffening layer 100 may beadded to the surface of substrate 12 prior to the imprint process. Theaddition of the stiffening layer 100 changes the overall geometry andstiffness characteristics of the substrate 12. This change in thesubstrate 12 properties results in reduced pulling stress and/orshearing stress during separation of the template 18 (not shown) and thesubstrate 12. In an exemplary embodiment, a predetermined thickness of astiffening layer 100 is added to the surface of substrate 12 that iscalculated to produce a desired geometry and/or desired stiffness and/orstress characteristics. The changes to the geometry, stiffness, and/orstress characteristics may result in a more robust layer separation,with fewer and/or smaller imprint separation defects.

For example, FIG. 6 is an illustration of two imprinted substrates; thefirst substrate 602 shows the results of imprinting on a substrate 12without a stiffening layer 100, and the second substrate 604 shows theresults of imprinting on a substrate 12 with a stiffening layer 100added prior to imprinting. As illustrated in FIG. 6, the regular wafer(substrate 602) without the stiffening layer 100 shows separationdefects at 630 and 632 resulting from the separation process. However,the wafer (substrate 604) with the stiffening layer 100 added to thesurface of the substrate 12 prior to imprinting shows no separationdefects.

Varying the Magnitude of Applied Forces

Matching strains when a template 18 has areas of varying feature densitypresents unique challenges. In an exemplary embodiment, the forcesapplied to the substrate 12 and the template 18 during the separationprocess may be varied or manipulated to achieve a more robust layerseparation.

FIGS. 7A and 7B illustrate template curvature and the correspondingshear strain of its surface depending on template feature density. Therelative curvature (indicated by the separation angle a) representsflexing of the substrate 12 (not shown) due to strain during separationfrom the template 18. Here, a change in strain and curvature occursbecause a larger force is required to overcome a greater friction force(in addition to an adhesion force) to separate the template 18 from thesubstrate 12 in a dense feature area 722 than in a sparse feature area720 and 724. Here, the separation angle a is shown in FIG. 7A as a₁ inthe sparse feature areas 720 and 724, and is shown as a₂ in the densefeature area 722.

Varying the forces applied to the substrate 12 and/or the template 18,as shown in FIG. 7B, (illustrated by F₁ and F₂) as separation progressesthrough variations in feature density may improve robust layerseparation.

In another embodiment, as illustrated by the graph in FIG. 8, separationbetween template 18 and substrate 12 may generally comprise two steps.In a step 82, the separation force F_(SEP) between template 18 may beincreased to a peak P. Such an increase may cause an initial crack inthe imprint field. For example, the increase in separation force F_(SEP)may cause an initial crack at one or more corners of the imprint field,starting the separation of the template 18 and substrate 12. In a step84, separation force F_(SEP) may be dramatically reduced. For example,the separation force F_(SEP) may be reduced from a maximum value tozero, or very low, in a very short amount of time. In one embodiment,the force reduction time is approximately 10 ms.

Referring back to FIG. 4, one embodiment varies applied forces tocontrol lateral motion of the template 18 with respect to the substrate12 during separation, to reduce, if not minimize shearing stress. Forexample, during the separation process, the template 18 may conform tothe features 50 in the un-separated area 440. The lateral motion betweentemplate 18 and features 50 may be constrained by the friction forcebetween template 18 and features 50. However, the imprint head 30 (asseen in FIG. 1) may also be affected by the friction force betweentemplate 18 and features 50. For example, imprint head 30 may beoverconstrained during the imprint process resulting in some energystorage in one or more elastic elements of the imprint head 30. Justbefore the last moment of separation between template 18 and substrate12, the friction force between template 18 and features 50 may bequickly reduced to zero. The stored potential energy within imprint head30 may be released at this time, which may result in relative xy-motionbetween template 18 and substrate 12.

FIG. 9 illustrates a process 90 (and refers to FIG. 10) of an exemplarymethod for separating template 18 from substrate 12 while minimizingshearing and pulling stress by limiting lateral displacement. In a step92, a predetermined pressure may be applied by chuck 28 to the template18. In a step 94, separation force F_(SEP) may be applied by imprinthead 30 to initiate separation of template 18 and patterned layer(solidified layer) 46. In a step 96, the separation force F_(SEP)applied by imprint head 30 may be monitored to a constant pullingstress. For example, forces applied to imprint head 30 may be monitoredas patterned layer 46 separates towards center C of template 18. In astep 98, chuck 28 may reduce the predetermined pressure applied totemplate 18. In a step 100, template 18 may be separated from patternedlayer 46.

Using this approach, curvature of the contact line 60 may be controlledat a level that may be tolerated by properties of polymerizable material34 and/or patterned layer 46, and then gradually reduced to zero withthe reduced pressure. For example, pressure applied to template 18 bychuck 28 may be balanced by stress forces caused by bending of template18 during separation. As pressure is reduced, these stress forces mayprovide for the separation of template 18 from patterned layer 46.

The pressure gradient provided by chuck 28 may generally be directedfrom high to low pressure (e.g., from inside of chuck 28 towardoutside), and may be perpendicular to patterning surface 22 of template18. As fluids generally are not able to support shear while in a staticstate, the separation force F_(SEP) may remain substantially normal tothe patterning surface 22. As such, z motion from imprint head 30 maynot be required during the final moments of separation of the template18 from the patterned layer 46. Thus, by controlling the forces appliedby imprint head 30 and the pressure applied by chuck 28, shearing loadbased on lateral displacement may be controlled during separation oftemplate 18 and patterned layer 46.

In an alternative embodiment, step 92 may be considered optional, giventhat chuck 28 need not apply the predetermined pressure to template 18prior to initiation of separation of template 18 and patterned layer 46.As such, partial vacuum pressure may be used to separate template 18from patterned layer 46 solely at the final moments of separation. Usingthis method, motion of contact line 60 during the final moments ofseparation may be independent of imprint head 30 motion. For example,vertical separation motion may be generated by template 18 and/orsubstrate 12 pressure or vacuum tracking control. As such, there may belimited shearing defects resulting from translation or rotation errormotion of the z separation mechanism. The shear strain resulting fromthe long range separation motion may be released by controlling theposition of imprint head 30 and/or relocating substrate 12. This mayreduce requirements for substantial accuracy during the separationmotion. Further, the lateral motion that may be caused by curvature oftemplate 18 may be minimized as deflection of template 18 at the finalmoment of separation is generally minimized.

Varying the Acceleration and Velocity of Applied Forces

In another embodiment, the acceleration and/or the velocity of appliedforces may be varied or modified to achieve robust layer separation ofthe template 18 and the substrate 12. Considering FIG. 10, the imprinthead 30 may pull the template 18 away from the substrate 12 at a highrate of acceleration. Due to inertia of the template 18 and substrate 12(their mass and also the inertia of air around the contact area), thedynamic template 18 and substrate 12 strains during acceleration will behigher than at a constant velocity. The inertial effect will result inextra strain energy stored in the template 18 and substrate 12 duringacceleration, similar to storing energy in a spring under similarconditions. This “spring” energy is converted to kinetic energy as thesystem reaches constant pulling velocity.

Increased strain at high acceleration may cause additional normal force,leading to additional friction. Though the steady state kinetic frictionhas weak velocity dependence, the transition from static friction forceto the kinetic friction force is described as an avalanche like process,being sensitive to the rate of the transition. The established kineticfriction force is generally less than the static friction force. Inother words, for a short time the resulting friction coefficient mayincrease. Also an attempt to move the template 18 fast (transition fromstatic position to the motion) may increase the static coefficient offriction (the so called limiting value). This occurs because not all thepoints of contact where the template 18 and the patterned layer 46attach to each other separate at the same time thereby resulting inextra separation energy being required. For example, this may occurduring separation of interdigitated or interlocked features in aslightly tilted direction. This extra separation energy may lead topattern damage, torn features, pull-ups and line collapse.

Since an increased friction force (and increased strain) is present withhigher acceleration of operation, the strains in the template 18 and thesubstrate 12 may be expected to decrease with a separation processoperating at a constant velocity or lower acceleration. In order tominimize the number of imprint defects, the separation velocity may beadjusted, modified, or varied in such a way that allows the frictionforce to be minimized during the separation process. In one embodiment,changes to the separation velocity are made while propagating separationof the template 18 and the substrate 12 through patterned regions ofvarying feature density. For example, the propagation velocity of thecrack (separation) may change abruptly when transitioning from an areahaving a dense feature pattern into an area having a less dense featurepattern. The reverse is also true. In the former case, an extra elasticenergy is released, thereby leading to abrupt acceleration of the crackvelocity (separation velocity). Transient regions having moments ofabrupt acceleration are more prone to imprint defects.

One of the ways to minimize transition region problems is to slow downthe separation of the template 18 and the substrate 12. For example, ifseparation normally takes 10 to 100 ms to complete, slowing down theseparation may comprise adjusting the process parameters in such a waythat separation will take twice as long to complete, i.e. 20 to 200 ms.Separation speed can be controlled by monitoring the separation forceapplied to the template 18 and intentionally lowering the applied force.Thus, in one embodiment, the separation is slowed to a user-determinedrate, thereby reducing or preventing surface bending and/or elasticenergy storage in the template 18 and/or the substrate 12. In anotherembodiment, the velocity of the separation is controlled, maintaining asteady separation velocity while the crack moves through the featurepattern boundary.

Monitoring and Feedback

Referring to FIG. 10, separation of the template 18 and the substrate 12may be monitored and/or tracked by analyzing the motion of the contactline 60 and/or the detection of the peak P separation force F_(SEP). Forexample, the motion of contact line 60 (e.g., curvature and length), maybe captured by imaging system 66. Imaging system 66 may be any systemcapable of providing macroscopic and/or microscopic views of patternedlayer 46. Some examples of imaging system 66 may include a web cam, avideo camera (tape, disc, or digital), a film camera (still or motion),a hyper-spectral imaging system (spectral interferometer), or the like.Imaging system 66 may be capable of providing still images and/or movingimages for analysis of prospective issues arising with regard topatterned layer 46. Imaging system 66 may also be capable of storing andrecalling still images and/or moving images, or transmitting them via acommunication system.

In an embodiment, tracking of the separation contact line 60 on apatterned layer 46 provides feedback on the magnitude orvelocity/acceleration of forces to apply at a given time. For example, afeedback control loop relative to an applied separation force F_(SEP)may be provided to a user and/or to an automated system. An automatedsystem receiving such feedback may automatically adjust the variousforces applied, including the magnitude, velocity, and acceleration ofvacuum, pressure, pulling force, and the like. Also, an automated systemreceiving such feedback may make adjustments to the physical componentsof the imprint system, including the tilt, alignment, rotation, angles,and the like of various components. Such control of the applied forcesand the physical components may improve robust layer separation withinpatterned layer 46.

FIG. 11 illustrates a flow chart of an exemplary method 110 forimproving robust layer separation by using feedback to control theseparation forces applied over a period of time. In step 112, aseparation force may be applied to initiate separation between template18 and substrate 12. For example, imprint head 30 may apply separationforce F_(SEP) to template 18 separating template 18 from patterned layer46. Such an application of separation forces may cause an initial crackbetween template 18 and patterned layer 46.

In step 114, the motion of contact line 60 (e.g., curvature and length)and/or peak P of separation forces may be monitored and/or tracked foranalysis of prospective issues arising with regard to patterned layer46. The monitoring and tracking may be performed by various imagingsystems 66.

In step 116, the strain properties of the substrate and/or the templatemay be analyzed based on the data gathered from the monitoring and/ortracking. Feedback may then be provided based on the monitoring and/ortracking, and the analysis performed.

In step 118, feedback from tracking of the contact line 60 and/or peak Pmay be used to adjust, modify, or vary the applied separation forces. Inone example, the amount of curvature of contact line 60 may bemonitored. If the curvature reaches a predetermined level or haspredetermined characteristics suggesting a probability of defects,various separation forces may be reduced, increased, or changes may bemade to their velocity, acceleration, direction of application, or thelike. In an exemplary embodiment, the adjusting, modifying, or varyingmay be performed automatically.

In step 120, results of the feedback information for separation betweentemplate 18 and patterned layer 46 may be stored and used to form analgorithm for future use and application in system 10.

Dummy Fill Patterns

As discussed earlier, the transition from a densely patterned region toa sparsely patterned region during separation represents a concern.Feature damage due to shear and cohesive failures have been observed tobe dominant at the transition region, where a change in separationvelocity due to feature density variation may lead to a change in stressexerted upon the fine features.

In many cases, so-called “dummy patterns” may be included in designs forintegrated circuit (IC) manufacturing to equalize etch loading andimprove chemical mechanical polishing (CMP). Dummy patterns areextraneous fill patterns included on a template 18, and are arrangedaround areas of critical or pertinent feature patterns on the template18. The use of dummy patterns may greatly improve robust layerseparation by reducing or eliminating occurrences of transitioningbetween areas of higher density feature patterns and lower densityfeature patterns, by filling in lower density feature areas withextraneous patterns. In order to reduce defects in an imprint process,the dummy pattern layout should take into account the proximity to thecritical dense features of interest, the size and shape required tominimize the jumps in elastic energy that may be experienced duringseparation, and a fill factor that is closely matched to the featurepattern of the critical patterned area. Also, it is desirable thatorientation and/or symmetry of the dummy pattern is selected to matchmechanical stresses experienced in the critical dense region. Within theconstraints of the design for device functionality, dummy patterns maybe placed as closely as possible to the field of the pertinent densepatterns. In one embodiment, the separation is no more than a fewhundred nanometers.

FIG. 12 illustrates various dummy fill options. As shown, a variety ofdummy patterns may be considered, for example, blocks, gratings, brokengratings, staggered rectangles, bi-directional rectangles, and the likemay be used. The fill factor or pattern density of the dummy pattern maytake into account the pattern being matched. In an exemplary generalrule, a 50% dummy pattern fill may be targeted.

In one embodiment, initial separation force may be reduced by varyingthe pattern density of the template 18. This may be accomplished using aserrated or wave-like pattern as a dummy fill on the mesa 20 portion ofthe template 18. Generally, the mesa 20 is substantially normal to thedirection of separation along a majority of the perimeter of theinterface 60. This orientation results in the need for a greater overallforce to initiate separation, since the strain along the perimeter isnearly equal everywhere.

In one embodiment, a serrated or wave-like mesa (with many smallserrations like on a postage stamp or knife blade) is used to helpinitiate separation of the template 18 and the substrate 12. Using aserrated or wave-like pattern as a dummy fill on the mesa 20 portion ofthe template 18 may allow the use of a lesser separation force toinitiate separation by concentrating the stresses along the smallserrations. The use of a lesser initial separation force may bebeneficial in improving robust layer separation by reducing the peakforce P applied during the separation process as discussed above, and byproviding greater control of forces applied throughout the separationprocess.

Chuck Pin Removal

In another embodiment, the chuck 28 apparatus may be modified or alteredto improve robust layer separation. The rigid template 18 may beconsidered as a beam with multiple supports. The supports do not changeas a force is applied to the template 18, so the template 18 strain isgenerally linear with an applied separation force. In contrast, thesubstrate 12 makes and breaks contact with various pins during theapplication of applied forces during the separation process. Further,the underneath “free span” region of the substrate 12, on which vacuumis applied, changes as force is applied to it; therefore, the substrate12 strain will generally be nonlinear with applied force.

The substrate 12 strain may be more linear if used with a pin-less waferchuck. Removing pins from the chuck 28 creates areas having more linearreaction to the forces applied. In one embodiment, a plurality ofpredetermined chuck pins are removed from the chuck 28 at criticalstress areas. In an embodiment, the predetermined chuck pins are thosethat are located at positions along the substrate 12 having the greatestnon-linear dependence of strain versus stress of the substrate 12. In afurther embodiment, the predetermined chuck pins are those in areas oflast contact points between the substrate 12 and the template 18 duringseparation. For example, non-linear strain-stress dependence may bereduced by removing chuck pins at the center area of the imprint and/ornear the last point of contact between substrate 12 and template 18. Amore linear separation increases robust layer separation, and mayminimize the possibility of defects on separation.

1. A method of patterning a substrate, comprising: matching strainproperties of the substrate to a template, the template having a firstrelief pattern; transferring a second relief pattern to the substratecorresponding to the first relief pattern on the template, thetransferring comprising forming the second relief pattern in a formableliquid between the substrate and the template corresponding to the firstrelief pattern on the template, the formable liquid forming a solidifiedlayer deposited on the substrate; and separating the template from thesolidified layer.
 2. The method of claim 1, wherein the substrate is animprint lithography substrate, and wherein the matching comprisesconforming a stiffness of the substrate to a stiffness of the template.3. The method of claim 1, wherein the matching comprises conforming athickness of the substrate to a thickness of the template.
 4. The methodof claim 1, further comprising applying a surplus formable liquidbetween the template and the substrate, the surplus formable liquidforming a residual layer, wherein the matching comprises matching thestrain properties by varying a thickness of the residual layer.
 5. Themethod of claim 4, wherein the matching comprises matching the strainproperties by increasing the thickness of the residual layer by apredetermined amount.
 6. The method of claim 1, further comprisingapplying a stiffening layer of predetermined thickness to the surface ofthe substrate prior to the transferring.
 7. The method of claim 6,wherein the stiffening layer is a Spun on Glass (SOG) layer.
 8. Themethod of claim 1, wherein the separating comprises modifying forcesapplied to at least one of the template and/or the substrate while thetemplate is being separated from the solidified layer.
 9. The method ofclaim 8, wherein the modifying comprises varying a pressure and/or avacuum force applied to the substrate, such that the strain propertiesof the substrate remain constant while the template is being separatedfrom the solidified layer.
 10. The method of claim 8, wherein modifyingcomprises varying a pressure and/or a vacuum force applied to the atleast one of the template and/or the substrate based on a featuredensity of the first relief pattern.
 11. The method of claim 8, whereinthe modifying comprises: increasing a pressure and/or a vacuum forceapplied to the at least one of the template and/or the substrate to apredetermined peak magnitude, and when an initial separation isdetected, reducing the pressure and/or the vacuum force applied to theat least one of the template and/or the substrate to a predeterminedminimum magnitude.
 12. The method of claim 8, wherein the modifyingcomprises modifying the forces applied to the at least one of thetemplate and/or the substrate such that the separation of the templatefrom the solidified layer occurs at a predetermined acceleration rate.13. The method of claim 12, further comprising modifying the forcesapplied to the at least one of the template and/or the substrate suchthat the separation of the template from the solidified layer occurs ata constant velocity.
 14. The method of claim 8, wherein the modifyingcomprises: applying a predetermined pressure to the template; applying aseparation force configured to initiate separation of the template fromthe solidified layer, the separation force to remain constant and normalto the solidified layer; and reducing the predetermined pressure appliedto the template.
 15. The method of claim 8, wherein the modifyingcomprises: applying a separation force configured to initiate separationof the template from the solidified layer, the separation force toremain constant and normal to the solidified layer; and applying avacuum to the at least one of the template and/or the substrate onceseparation has commenced.
 16. The method of claim 1, wherein theseparating comprises: monitoring forces applied to at least one of thetemplate and/or the substrate while the template is being separated fromthe solidified layer; analyzing the strain properties of the substrate;providing feedback based on the analyzing; automatically adjusting theforces applied to the at least one of the template and/or the substratebased on the feedback received.
 17. The method of claim 16, wherein themonitoring is performed by a hyper-spectral imaging system configured toobtain real-time images at various discrete wavelengths.
 18. A method ofpatterning a substrate, comprising: matching strain properties of thesubstrate to a template, the template having a first relief pattern,wherein the first relief pattern includes extraneous fill patternspositioned adjacent to pertinent patterns; transferring a second reliefpattern to the substrate corresponding to the first relief pattern onthe template, the transferring comprising forming the second reliefpattern in a formable liquid between the substrate and the templatecorresponding to the first relief pattern on the template, the formableliquid forming a solidified layer deposited on the substrate; andseparating the template from the solidified layer.
 19. The method ofclaim 18, wherein the extraneous fill patterns comprise serrationsconfigured to initiate separation of the template from the solidifiedlayer.
 20. A method of patterning a substrate, comprising: matchingstrain properties of the substrate to a template, the template having afirst relief pattern; transferring a second relief pattern to thesubstrate corresponding to the first relief pattern on the template, thetransferring comprising forming the second relief pattern in a formableliquid between the substrate and the template corresponding to the firstrelief pattern on the template, the formable liquid forming a solidifiedlayer deposited on the substrate; removing a plurality of predeterminedchuck pins from a substrate chuck, wherein the plurality ofpredetermined chuck pins are located at positions having the greatestnon-linear dependence of strain versus stress of the substrate; andseparating the template from the solidified layer.